When drilling wells, such as oil wells, a drilling fluid is circulated in the well during drilling operations. The drilled formations have fractures or high permeability which sometimes allows the drilling fluid to dissipate into the formation causing a loss of drilling fluid and lost circulation during drilling operations. Materials added to the drilling fluid to stop the loss are called lost circulation materials or additives. Many lost circulation materials consisting of varying combinations of flakes, fibers and granules have been used and described in the art. For example, U.S. Pat. No. 3,375,888 teaches the use of nutshells, shredded carpet and lacquered regenerated cellulose in a three component system to prevent or restore lost circulation.
While such mixtures described in the prior art does have some advantages, the mixtures presently available leave much to be desired in a particularly important area.
A lost circulation material is described in U.S. Pat. No. 3,574,099 which pins its success upon nutsells and asbestos fibers. The patentee states that there is no fibrous alternative to asbestos fibers. Further, U.S. Pat. No. 3,629,102 describes a three component mixture of nutshells (course and finer) and sugar cain fibers. Many other patent disclosures were discussed of the above-mentioned disclosure.
The problem with the materials used and described in the prior art thus far is that once the permeability of a formation has been sealed by whatever materials used, the formation cannot be reopened to achieve satisfactory permeability for oil production. Many times when lost circulation occurs, it may be into the intended producing formation itself. When this occurs with a lost circulation material in the system, the potential producing formation is sealed off, permeability reduced and production of oil from the formation becomes more difficult. The formation can only be reopened and permeability restored with difficulty.
The lost circulation material of this invention not only provides a material that will seal both formation fractures and permeable formations, it, more importantly, accomplishes this using a material that can be degraded using an acid without damaging the potential producing formation. By providing a soluble or degradable lost circulation material, the seal that is formed on the face of the producing formation can be reopened to allow the formation to produce. No prior art has thus far disclosed such a composition of material to effectuate the desired degradation. In fact, some prior art, casts doubt that the components of the composition of this invention are even satisfactory for use to prevent or stop the loss of circulation during drilling operations.
This invention provides a material which degrades upon contact with an acid that will not interfere with the production process of the well itself. Ideally, the seal breaking process should be compatible with the well production process.